New data: tamoxifen takers may gain efficacy/tolerability benefits from switch to anastrozole adjuvant therapy

New data: tamoxifen takers may gain efficacy/tolerability benefits from switch to anastrozole adjuvant therapy

NOTTINGHAM, U.K., September 17, 2003 -- New trial findings indicate that patients who have their adjuvant therapy changed from tamoxifen to 'Arimidex' (anastrozole) are less likely to experience a relapse of the disease than patients who remain on tamoxifen. Furthermore, changing therapy to anastrozole resulted in fewer serious adverse events than continued tamoxifen treatment (1).

The data, presented at the 8th International Nottingham Breast Cancer Conference, provide further evidence of the superior overall risk:benefit profile of anastrozole over tamoxifen in the adjuvant treatment of postmenopausal women with hormone-responsive early breast cancer.

The ITA (Intergruppo Tamoxifen 'Arimidex') study is the first since the landmark ATAC ('Arimidex', Tamoxifen, Alone or in Combination) trial to compare the efficacy and tolerability of anastrozole with that of tamoxifen in the adjuvant treatment of hormone-responsive early disease. Based on 47 months follow up from the ATAC trial, anastrozole has already been shown to offer superior efficacy compared to tamoxifen, with a number of important tolerability advantages (2). The ATAC data demonstrate that, for newly diagnosed patients, adjuvant anastrozole treatment is a preferable alternative to tamoxifen.

The promising new data from the ITA trial, however, indicate that patients currently taking tamoxifen may also gain benefits -- in terms of both efficacy and tolerability -- if their therapy is switched to anastrozole. Taken together, the ITA and ATAC data provide support for the use of anastrozole as an adjuvant therapy option for all postmenopausal women with hormone-sensitive disease, whether they are newly diagnosed or already receiving tamoxifen. Furthermore, they question the position of tamoxifen as the preferred endocrine treatment option in this setting.

Although the ATAC trial remains the largest breast cancer trial ever conducted, with over 9,300 participants from over 21 countries around the world, the study only recruited women who had not previously taken endocrine therapy. Therefore the data could not provide guidance on the most appropriate treatment for those women who had already commenced tamoxifen therapy. The ITA trial, involving 449 Italian patients, was set up to answer this question, i.e. to establish if the benefits of anastrozole over tamoxifen would still be seen in patients switched to anastrozole who had already commenced their adjuvant therapy with tamoxifen.

The initial findings indicate that even after two to three years of tamoxifen therapy, patients who then change to anastrozole appear to benefit from a longer disease-free survival and fewer serious adverse events than those women who remain on tamoxifen. Based on 24 months' follow-up from the point of randomisation to change to anastrozole or continue on tamoxifen, those patients who changed therapy to anastrozole were less likely to suffer disease recurrence and were also less likely to experience drug-related serious side effects (such as endometrial cancer or thromboembolic complications) than those who remained on tamoxifen (1).

Commenting on the importance of these new data, lead trial investigator Dr F Boccardo of the University and National Cancer Research Institute in Genoa, Italy, said: "We are very excited by these trial results as they help to answer the question that many clinicians have asked since the publication of the ATAC data, 'what if my patients are already taking tamoxifen?'. The data indicate not only that a switch from tamoxifen to anastrozole is viable, but also that such a change in therapy appears to result in a reduced risk of disease recurrence and fewer serious side effects."

Tamoxifen is associated in some women with an increased risk of endometrial cancer, deep vein thrombosis (DVT) and other serious side effects (2). Until the first publication of the ATAC trial results in 2001, there were no data to support an alternative endocrine treatment option in the adjuvant setting. Consequently, many women have already embarked on the recommended five-year course of adjuvant tamoxifen. The results of the ITA trial suggest that these women may benefit by changing their therapy to the newer drug, anastrozole.

Commenting on this point, Professor Jeffrey Tobias of London's University College Medical School and University College Hospitals said: "In my view, these new data are extremely important. They imply that patients already taking tamoxifen may also be candidates for treatment with anastrozole and this is the first time we have been in a position to make such as statement. These data certainly add to the growing body of evidence supporting the use of anastrozole in the adjuvant setting."

References:

1. AstraZeneca Pharmaceuticals' Data on File
2. The ATAC ('Arimidex', Tamoxifen, Alone or in Combination) Trialists' Group. Anastrozole alone or in combination with tamoxifen versus tamoxifen alone for adjuvant treatment of postmenopausal women with early breast cancer: results of the ATAC trial efficacy and safety update analyses. Accepted for publication; Cancer 2003.

Anastrozole ('Arimidex') is a trademark, property of the AstraZeneca Group of Companies.

Product background:

• Anastrozole -- marketed by AstraZeneca as 'Arimidex' -- is approved world-wide for postmenopausal women with advanced disease. The drug is also already approved as an adjuvant treatment for postmenopausal women with hormone receptor-positive early breast cancer in 25 countries, including the U.S., U.K., Germany, Italy, and Spain.
• Anastrozole is a potent, highly selective, non-steroidal oral aromatase inhibitor used in the hormonal (endocrine) treatment of breast cancer in postmenopausal women.
• Tamoxifen -- marketed by AstraZeneca as 'Nolvadex' -- is an anti-estrogen and acts primarily to prevent estrogen binding to its receptor at tumour sites. Tamoxifen has some partial estrogenic activity, which may be responsible for the differences in its side-effect profile compared with anastrozole.
• Anastrozole acts differently from tamoxifen by blocking the production of estrogen by the aromatase enzyme pathway -- the primary source of estrogen in postmenopausal women whose ovaries no longer function.
• The current treatment strategy for hormone-sensitive early-stage breast cancer (cancer that has not spread beyond the breast) in postmenopausal women generally consists of initial surgery to remove the tumour, which may be followed by a course of chemotherapy and/or radiotherapy. Women will usually then go on to take a hormonal drug treatment -- such as tamoxifen or anastrozole -- for around five years, to reduce the risk of the cancer recurring (this is known as "adjuvant therapy"). 

Source: AstraZeneca

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